1. Field of the Invention
The present invention relates to circuits and methods for protecting motherboards, and more particularly to a circuit and a method for protecting a motherboard of which a CPU power header is disconnected from a power supply thereof.
2. Description of Related Art
A conventional computer generally includes an ATX power supply with a 20-pin main power connector, and a 4-pin power connector both of which connect to a motherboard thereof. The 4-pin power connector provides a +12V working voltage to a CPU of the motherboard after the power supply is turned on. If an operator carelessly leaves the 4-pin power connector disconnected from a CPU power header on the motherboard when the computer is assembled, the CPU of the motherboard will not be able to run after the computer is turned on. The motherboard and/or its components may be damaged due to this unintentional disconnection.
In order to protect the motherboard from damage due to the unintentional disconnection, a protection circuit is provided as shown in FIG. 1. The circuit includes a first transistor Q1, a second transistor Q2, and a third transistor Q3. A base of the first transistor Q1 receives a CPU power signal, and an emitter is connected to ground. A base of the second transistor Q2 is connected to a collector of the first transistor Q1, an emitter is connected to ground, and a collector is configured to receive a PWRBTN# signal which is at high level after the computer is on or off and goes low to switch the computer off or on. An emitter of the third transistor Q3 is connected to the collector of the first transistor Q1, a base receives a PWROK signal, which switches from low to high level after the computer is turned on, and a collector is supplied with a +5V voltage source after the computer is turned on. When the computer is turned on without there being a connection with a CPU power connector of a power supply thereof, the first transistor Q1 is closed. The second and third transistors are turned on due to a high level PWROK signal to ground the PWRBTN# signal for switching off the computer and protect the motherboard from damage due to abnormal CPU power-on voltage applied thereto.
However, the PWRBTN# signal switches off the computer via a power controller which directly turns off the power supply of the computer after a 4 second delay when the PWRBTN# signal is grounded and goes from high to low level if no power-on voltage for CPU is provided. Therefore, the motherboard is still at risk during that delay time.
What is needed, therefore, is a circuit to power off the computer more quickly when the computer is turned on without normal CPU power to a motherboard thereof.